Evaluation of commercially available tests for Chlamydia nucleic acid detection in synovial fluid of patients

Since the presence of Chlamydia nucleic acids has been shown in synovial fluid (SF) from some patients with Chlamydia reactive arthritis, we investigated whether commercially available tests, developed to detect Chlamydia nucleic acids in urogenital samples, could also be used for their detection in SF samples. We therefore tested SF samples, found positive with at least two different systems of DNA amplification in a previous study, with three commercially available kits. No positive results were obtained. It is concluded that the commercially available tests Gen-Probe PACE 2, Amplicor (developed by Roche Molecular Systems) and LCx (developed by Abbott Laboratories) do not have sufficient sensitivity to detect reliably Chlamydia RNA or DNA in S

The Ralstonia solanacearum pathogenicity regulator HrpB induces 3-hydroxy-oxindole synthesis

The transcriptional activator HrpB of the bacterial wilt causing betaproteobacterium Ralstonia solanacearum represents a key regulator for pathogenicity. In particular, it drives expression of hrp genes encoding a type III secretion system (T3SS) as well as effector molecules for delivery into the host cytosol to promote disease. However, the HrpB regulon extends beyond this T3SS. We describe here an HrpB-activated operon of six genes that is responsible for the synthesis of a fluorescent isatin derivative of 149 Amu that we named HDF for HrpB-dependent factor and that we purified from culture supernatants. The structure of the labile molecule was solved by using NMR and CD spectroscopy to be (3S)-3-hydroxy-indolin-2-one and confirmed by its chemical synthesis and MS spectrometry. HDF was found to be present at 20 nM in wild-type cultures grown on minimal medium, and its synthesis increased 15-fold upon overproduction of HrpB, confirming that HrpB activates HDF synthesis. The addition of tryptophan significantly stimulated HDF biosynthesis and was shown to represent the precursor molecule for HDF synthesis. A search for the biological function of the molecule revealed that HDF induces acyl-homoserine lactone receptor-mediated reporter activity of the well studied LuxR transcriptional regulator of Vibrio fischeri. Thus, our results provide evidence that the specificity of acyl-homoserine lactone (acyl-HSL) receptors is clearly broader than previously considered. The failure to detect induction by HDF of the described endogenous quorum-sensing circuits of the pathogen points to a role in interfering with cell–cell signaling of rivalling bacteria

Biosynthesis of a Complex Yersiniabactin-Like Natural Product via the mic Locus in Phytopathogen Ralstonia solanacearum▿†

A genome mining study in the plant pathogenic bacterium Ralstonia solanacearum GMI1000 unveiled a polyketide synthase/nonribosomal peptide synthetase gene cluster putatively involved in siderophore biosynthesis. Insertional mutagenesis confirmed the respective locus to be operational under iron-deficient conditions and spurred the isolation of the associated natural product. Bioinformatic analyses of the gene cluster facilitated the structural characterization of this compound, which was subsequently identified as the antimycoplasma agent micacocidin. The metal-chelating properties of micacocidin were evaluated in competition experiments, and the cellular uptake of gallium-micacocidin complexes was demonstrated in R. solanacearum GMI1000, indicating a possible siderophore role. Comparative genomics revealed a conservation of the micacocidin gene cluster in defined, but globally dispersed phylotypes of R. solanacearum